Great article discussing in detail the temperatures and risks to cell health. It seems that in overall conclusion as temperatures reach 40 degrees and above, cells are affected. The risks are not just the temperatures but the frequency of such temperatures. When frequency is involved it seems that the smaller risks posed by not such extreme temperatures are still to be considered. Also to consider here that it's noted that skin cells are much more fragile and often forgotten, but exposed to such temperatures will affect these cells greatly.
Take a read!
https://www.ncbi.nlm.nih.gov/m/pubmed/9202452/

The research keeps coming!
This evidence shows that bandages and insulating boots speed time to leg warm up - the question here is if left on for longer, how much hotter to the legs get? Previous research with Katie Baxter discusses the fact that there is potentially no limit to temperature increase, demonstrated at only 15min!
Take a read!
https://www.researchgate.net/publication/261137365_Effect_of_a_bandage_or_tendon_boot_on_skin_temperature_of_the_metacarpus_at_rest_and_after_exercise_in_horses

Great simple article to explain reasons as to why your horse’s legs may be swelling in the stable.
Interesting also that bandaging suggested to potentially exacerbate this. Thoughts could be restriction of lymphatic flow and blood flow, over heating of legs, and infection through fungal and bacterial build up in warm damp conditions.
Take a read and let your thoughts flow!
https://www.thesprucepets.com/stocked-up-legs-in-horses-1885853